Application Layer | List of Protocols at the Application Layer | Web Technologies

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list of protocols in application layerList of Protocols and their use at
the Application Layer protocol,
Web Technologies Notes| Sixth Semester,
BSc.CSIT | Tribhuvan University (TU)

Application Layer
Application layer is an abstraction layer that specifies the shared protocols and interface method used by hosts in a communication network. The application layer abstraction is used in both of the standard models of computer networking: the Internet Protocol Suite (TCP/IP) and OSI model. Although both models use the same term for their respective highest level layer, the detailed definitions and purposes are different. There are many application layer protocols used in the internet like DNS, DHCP, IMAP, NTP, POP, RTP, SMTP, Telnet, TLS/SSL, XMPP etc. Detail description and use of some of the protocols of application layer are;

  • FTP (File Transfer Protocol): FTP is the standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture and uses separate control and data connections between the client and the server
  • HTTP (Hypertext Transfer Protocol): HTTP is the foundation of data communication for the World Wide Web (WWW). This protocol functions as a request-response protocol in the client-server computing model. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, returns a response message to the client. HTTP is designed to permit intermediate network elements to improve or enable communications between clients and servers.
  • SMTP (Simple Mail Transfer Protocol): SMTP is an internet standard for electronic mail transmission. Electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, while user level client mail applications typically use SMTP only for sending messages to a mail server for relaying. For retrieving messages, client applications usually use either IMAP or POP3.

World Wide Web (WWW)
WWW is a system of interlinked hypertext documents accessed via the Internet. The World Wide Web, or simply Web, is a way of accessing information over the medium of the Internet. It is an information-sharing model that is built on top of the Internet. It is a hyper media based web/infrastructure of information which made the already existing internet so user-friendly and hence extremely popular. The Web uses the HTTP protocol, only one of the languages spoken over the Internet, to transmit data. Web services, which use HTTP to allow applications to communicate in order to exchange business logic, use the Web to share information. The Web also utilizes browsers, such as Internet Explorer or Firefox, to access Web documents called Web pages that are linked to each other via hyperlinks. Web documents also contain graphics, sounds, text and video.

The Web is one of the services that runs on the Internet. It is a collection of textual documents and other resources, linked by hyperlinks and URLs, transmitted by web browsers and web servers. The Web is just one of the ways that information can be disseminated over the Internet, so the Web is just a portion of the Internet. In short, the Web can be thought of as an application “running” on the Internet.

It is a client/server oriented technology which has contributed a lot in the rapid growth of the use of the internet. One of the greatest advantages of WWW  technology is the capability of accessing and transfer of information across the inter connected computer networks. Ease of use, connectivity and compability with wide ranging technology is another plus point of this technology.

WWW has been central to the development of Information age and is the primary tool billions of people use to interact with the Internet. The hyperlink structure of the WWW is described by the webgraph, the nodes of the web graph correspond to the web pages, the directed edges between them to the hyperlink.

To make web pages interactive some web app use JS techniques like Ajax. Client-side script is delivered with the page that can make additional HTTP requests to the server, either in response to user actions such as mouse movements or clicks or based on elapsed time. The server’s response are used to modify the current page rather than creating a new page. So the server needs only to provide limited incremental information.

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